Home About IEF Conferences Newsletter Resources e-learning centre on sustainable development IEF SUSTAPEDIA AN ENCYCLOPEDIA OF SUSTAINABILITY

The collapse of the North-west Atlantic cod fishery, among other ocean fishery crises and disputes, has only confirmed the concerns behind the oceans chapter of Agenda 21 (UNCED, 1992, para. 17.45 and 17.72). World fishery production has reached 122 million tones in 1997, a figure six times that of 1950 (FAO Fact File). Major ocean fisheries, most of which are within exclusive economic zones, are already using a high proportion of the total available primary production, amounting to 25 percent for upwelling areas and 24-35 percent in shelf systems, leaving little or no possibility for further increases in these most productive fisheries (Pauly and Christensen, 1995).  On the contrary, 70 percent of marine fisheries are so heavily exploited that reproduction cannot or can just barely keep up (Garcia, 1995). For example, the swordfish in the North Atlantic Ocean has declined by about 70% over the past twenty years and populations of cod, hake, haddock and flounder have fallen by as much as 95% between 1989 and 1994 (Jackson, 1995). In addition, large oceanic driftnets and longlines harvest not only the targeted fish species but slaughter numerous other species, such as dolphins, sharks, sea turtles and sea birds. One quarter of the world's annual catch (20 million tonnes) is thrown back into the sea, dead or dying (Leong Ching Ching, 1998). With the continuing over-investment in fishing fleets, annual losses now amount to $50 billion, requiring cuts of 20 to 50 percent in the fishing industry capacity to achieve sustainability (FAO Fisheries Department, 1995; Garcia, 1995).

Bottom trawling accounts for more of the world's catch than any other method, but due to its environmental impact, it is often compared to forest clear-cutting (Watling et al., 1998). The area trawled each year is about equivalent to 150 times the total forest area clear-cut yearly and corresponds to about an area twice the size of the contiguous United States (Norse, 1998). Until the 1950's, some areas were naturally protected from trawling, being too rocky, too deep or too remote to allow access (MCBI website), but today new technologies have permitted trawling almost everywhere. In intensive fishing areas, the bottom can be trawled 100 to 700% each year. Both bottom trawling and scallop dredging dramatically affect marine ecosystems. The large weighted nets not only catch all marine life in midwaters, whether targeted or caught incidentally, but also cause severe seabed habitat destruction. Sea creatures living on the bottom are crushed, buried or exposed to predators, and clouds of sediments rise, altering seabed biochemistry.
  

Healthy cobble-shell bottom habitat for scallops before (left) and after (right) one pass of a scallop dredge. No Javascript Before photo: Peter Auster, National Undersea Research Center. After photo: Peter Auster, NURC. (AOC website)

Shrimp trawl catch. The 95% of the catch in this photo that was not shrimp died on deck and was shoved overboard. (Elliott A. Norse). (MCBI website).

The total world aquaculture production contributes to the global fish supply. Aquaculture is one of the fastest growing food sectors, with production increasing from 10 million tonnes in 1990 to 29 million tonnes in 1997 (FAO, 1999). More than 220 species of finfish and shellfish are farmed today.

However, carnivorous farmed fish are fed on high levels of fish meal and fish oil and require a fish biomass input superior to the fish biomass produced. For the ten species of fish most commonly farmed , an average of 1.9kg of wild fish is required for every kilogram of fish raised. Unfortunately, there is an increase in the production trend of carnivorous fish (such as salmon or shrimp), rather than herbivorous or filter feeder fish. Small pelagic fish mainly provide the fish meal and fish oils used for aquaculture feed. Aquaculture's growing needs increase pressures existing on wild fisheries for small pelagic fish, which already suffer from overexploitation and are strained by climate changes resulting from the El Niño warming effect.

Aquaculture activities also result in indirect pressures on wild fisheries. Aquaculture farms have replaced hundreds of thousands of hectares of mangroves and coastal wetlands, which naturally provide nurseries and shelter for wild fish populations. In addition to natural habitat destruction, some farms remove wild finfish or shellfish post-larvae to stock their ponds, instead of using hatchery-reared post-larvae, thus affecting wild population renewal. Another problem may arise from the escape of farmed fish, which can cause serious biological pollution. Wild population genetics may be altered through hybridization with farmed individuals, and movement of cultured stocks may increase the risks that pathogens will spread to wild populations. Aquaculture fisheries may finally damage the environment through effluent discharge of untreated wastewater. Specialists recommend farming expansion of low trophic level fish with herbivorous diets and a reduction of fish meal and oil input in aquaculture feed. Polyculture is encouraged as a mean of exploiting all available food and water resources of the pond ecosystem (Naylor et al., 2000).
 

Fig 1: Data source: FAO website	Fig 2: Data source: FAO website

Links

Watch a video about the effect of bottom trawling or visit the website of the AOC: http://www.americanoceans.org/fish/pub.htm